The flu vaccine is a vaccine to protect against the highly variable Influenza virus.

Each year the influenza virus changes and different strains become dominant. Due to the high mutability of the virus a particular vaccine formulation usually only works for about a year. The World Health Organization co-ordinates the contents of the vaccine each year to contain the most likely strains of the virus to attack the next year. The flu vaccine is usually recommended for anyone in a high-risk group who would be likely to suffer complications from influenza.

Injectable flu vaccine is grown in fertilized chicken eggs whereas the new FluMist nasal spray vaccine produced by MedImmune is grown in chick kidney cells. FluMist is more effective and the recommended type of flu immunization for all healthy people ages 5 to 49, however, it contraindicated for those with allergy to egg or chicken proteins.

The production of flu vaccine requires a lead time of about six months before the season. It is possible that by flu season a strain becomes common for which the vaccine does not provide protection. In the 2003-2004 season the vaccine was produced to protect against A/Panama , A/New Caledonia , and B/Hong Kong . The strain A/Fujian was discovered after the vaccine was in production therefore did not provide protection against this strain.

On October 5, 2004, Chiron Corporation, a corporation contracted to deliver half of the expected flu vaccine for the United States and a significant portion to the UK, issued a press release [1] that stated it was unable to dispense its stock for the 2004-2005 season, due to suspension of the corporation's license to produce the vaccine by the Medicines and Healthcare Products Regulatory Agency. However, the Centers for Disease Control and Prevention took action to enlist the help of other companies such as MedImmune and Aventis Pasteur to supply the vaccine in high-risk populations in the United States and urged healthy people between the ages 5 and 49 to opt for the new FluMist nasal spray vaccine.

Health Controversy

In the late 1990s, a controversy arose from the use of thimerosol, a preservative containing mercury, in injectable vaccines. This preservative was proported to have a link to autism. However, flu vaccine is not routinely administered to children under the age of 2, and scientific evidence does so far not support a link between autism and injectable vaccines.